is for immersion of a heated manufactured steel part, such as a gear or axle, in a fluid to achieve rapid and uniform also called heat treating oil; it is used to cool metal parts during their manufacture, and is often preferred to water because the oil’s slower heat transfer lessens the possibility of cracking or warping of the metal. A quenching oil must have excellent oxidation stability and thermal stability , and should yield clean parts, essentially free of residue. In refining terms, a quenching oil is an oil introduced into high temperature vapors of cracked (see cracking) petroleum fractions to cool them.

Also see quenching.